The present invention relates to a joint device which is attached to each of arm units, constituting a arm of a robot, and is used to connect an arm unit and another arm unit adjacent thereto, and to rock the arm units.
In nuclear fuel reprocessing plants, facilities, such as tower tanks, nuclear reactors, fusion reactors, shielding cells, etc., have neither an entrance nor a space large enough to allow technical personnel to enter or work in. Also, these facilities are subject to harmful radioactive rays and the like. Usually, therefore, the personnel cannot directly enter the facilities to check them or work therein. With these facilities, it is necessary that the working person locate himself at a safe site and remotely operate a robot, situated in the facilities, or be allowed to enter them through a small entrance to work therein.
As shown in FIG. 1, for example, a robot may be used to inspect a spot which is unaccessible to the personnel. Entrance 202 is connected to object 201 of inspection, such as a tank. Robot 203 is inserted into tank 201 through entrance 202. Robot 203 is a multijoint robot having arm 205 which is composed of a plurality of arm units 204. Each unit 204 is coupled to its adjacent arm unit 204 by means of joint device 206. Device 206 allows the adjacent arm units to rock. Television camera 207, used for inspection inside tank 201, is attached to the distal end of arm 205. Arm 205 is supported by supporting device 208, which is moved up and down by means of lift deice 209. Control device 210 for controlling robot 203 is located outside tank 201.
Conventionally, a joint device is constructed as follows. It comprises a coupling mechanism and an arm unit rocking mechanism which are arranged so that an arm unit and another arm unit adjacent thereto are rotatable in a predetermined direction. The arm-unit rocking mechanism includes a semicircular gear for rocking the arm units, a gear train used to transmit a rotatory force to the semicircular gear, and a motor for supplying the rotatory force to the gear train. Thus, if the motor is driven, its rotatory force is transmitted to the semicircular gear through the gear train. The semicircular gear causes the one arm unit to rock relatively to the other arm unit, in the predetermined direction.
One or a plurality of joint devices may sometimes get out of order during an inspection in a tank. More specifically, the motor may be disabled, or otherwise, gear teeth or bearings for the gears may be broken or fail.
If the joint devices thus get out of order, the robot is removed from the tank and repaired. In this case, the arm units should preferably be free to rotate relatively to one another. In case of such a trouble, however, the output shaft of the motor is disabled from rotating due to its regenerative braking. Moreover, the reduction ratio of the gear train is so high that the motor shaft, gear train, and semicircular gear are restrained from rotating. In consequence, the rotation of the arm units is restrained, that is, one arm unit is not free to rotate relatively to another.
Accordingly, the arm units engage the inner surface of entrance 202, so that robot 203 sometimes cannot pass through the entrance. In some cases, therefore, it is difficult to remove robot 203 from tank 201.
If a plurality of joint devices get out of order when arm 205 is arcuated as shown in FIG. 1, in particular, robot 203 can hardly be removed from tank 201 through straight entrance 202.